VOL. LXXVI.] 



PHILOSOPHICAL TRANSACTIONS. 



117 



(Exp. N° 23.) 



Thermometer N^ 4. 



Surrounded by water. 



Taken out of freezing water, and 



plunged into boiling water. 



Heat acquired. 



10° 



20 



30 



40 



50 



60 



70 



80 



1 57 = total time of heating 

 from 0° to 70°. 



(Exp. N° 24, 25, and 26.) 



Thermometer N° 4. 



Surrounded by mercury. 



Taken out of freezing water, and planged into boiling 



water. 



The total times of heating from 0° to 70° in the 3 experiments with mercury 

 being 41 seconds, 31 seconds, and 48 seconds, the mean of these times is 40 

 seconds ; and as in the experiment with water the time employed in acquiring the 

 same degree of heat was 1™ 57^= 117 seconds, it appears from these experi- 

 ments, that the conducting power of mercury to that of water, under the circum- 

 stances described, is as 40 to 117 inversely, or as 1 000 to 342. And hence it is 

 plain why mercury appears so much hotter, and so much colder, to the touch 

 than water, when in fact it is of the same temperature : for the force or violence 

 of the sensation of hot or cold depends not entirely on the temperature of the 

 body exciting in us those sensations, or on the degree of heat it actually possesses, 

 but on the quantity of heat it is capable of communicating to us, or receiving 

 from us, in any given short period of time, or as the intensity of the communi- 

 cation ; and this depends in a great measure on the conducting powers of the 

 bodies in question. The sensation of hot is the entrance of heat into our bodies; 

 that of cold is its exit ; and whatever contributes to facilitate or accelerate this 

 communication adds to the violence of the sensation. And this is another proof 

 that the thermometer cannot be a just measure of the sensible heat or cold exist- 

 ing in bodies ; or rather, that the touch does not afford us a just indication of 

 their real temperatures. 



